1. Field of the Invention
The present invention relates to a robotic vehicle with a vehicle tracking system, more specifically, the present invention relates to a suspended carriage system for improved ded-reckoning of robotic vehicles.
2. Background Information
Ded-reckoning, often called dead-reckoning in error, is a shortening of the term deduced reckoning. Deduced reckoning refers to a guidance or navigational system used to calculate the position of a moving object. Originally, sailors used to calculate their position by knowing where they started, and knowing the direction and the speed at which they were traveling. Deduced reckoning is the calculating of the current or updated position of an object based upon factors associated with movement of the object such as the direction of travel, the speed of travel and the time spent traveling in specific directions. The resulting calculated current position of the object is an approximation, and occasional corrections are made based upon known landmarks. Known landmarks could essentially be utilized to reset the starting position for subsequent updating by ded-reckoning techniques.
Robotic vehicles have utilized ded-reckoning systems to keep track of their location. For example, gantry style industrial robots use ded-reckoning techniques for calculating the location of the robotic carriage. Gantry style robots utilize a gear in a rack for movement of the robotic carriage. The rack is fixed and the gear causes the robotic carriage to travel along the length. The position of the robotic carriage is calculated by knowing how many revolutions the gear has turned and knowing the starting position of the robotic carriage. In a gantry style robot, the ded-reckoning positioning system can maintain an accuracy of up to 0.007 inches.
Ded-reckoning positioning systems can be utilized for tracking the Cartesian position of a wheeled vehicle as well. For any small incremental motion of each wheel, a new position and orientation can be calculated based upon the previous position and incremental rotation of each wheel. If the increments approach zero in length and the wheels maintain point contact with the road surface without slipping, the tracking error can be zero. However, the reality is that for any wheeled vehicle the contact with the floor is not a point but is a patch. Furthermore, slippage between the respective wheels and the flooring is inevitable. The slippage of the wheels is a result of the side forces generated on the wheels of the vehicle. Three elements cause side forces in wheels of a vehicle. First is acceleration; second is rolling resistance; and third is air friction. In certain applications, the acceleration and air friction can be minimized, leaving the rolling resistance as the primary contributor to side forces causing wheel slippage. The rolling resistance can be broken down into two components: rolling resistance of the powered wheel, and any other resistance caused by other contact between the vehicle and the surface. Rolling resistance of the powered wheel is always in the direction opposing the wheel and can be modeled mathematically. The larger, and more difficult to model, resistance associated with wheeled vehicles is that of a third or fourth point of contact between the vehicle and the floor which can exert forces in any direction on the powered wheel.
Robotic vehicles utilizing ded-reckoning as positioning systems have not satisfactorily eliminated wheel slippage, resulting in unacceptable error in the ded-reckoning positioning or tracking system. Consequently, the prior art robotic vehicles required frequent landmarks or methods of updating the position.
It is an object of the present invention to overcome the aforementioned drawbacks of the prior art. It is a further object of the present invention to provide a suspended carriage system for a robotic vehicle for improved ded-reckoning. A further object of the present invention is efficiently using ded-reckoning positioning systems for tracking robotic vehicle position. A further object of the present invention is to provide a simple control mechanism for manipulating a robotic vehicle position using a graphic interface. A further object of the present invention is to develop a robotic wheel design which minimizes error introduced into the robot positioning or tracking system. A further object of the present invention is to provide a ded-reckoning based robotic vehicle tracking system which compensates for wheel slippage. A further object of the present invention is to provide a simple calibration method for a robotic vehicle tracking system. A further object of the present invention is to provide a robot attaching harness for auxiliary equipment which minimizes error introduced into the robot positioning or tracking system.